Several methods and fastening devices have, in the past, been used to lock or seal two substrates to one another in order that they will resist mechanical separation, or form a liquid or airtight seal to prevent the flow or escape of fluids.
In particular, fastening devices have been proposed, or used, which employed adhesives or plastics in one way or another in order to prevent the fasteners from loosening during use or service. Early locking compositions were applied in liquid form shortly before assembly of the inter-fitting parts. However, in order to facilitate the high rates of assembly of the mass-production engineering industries such as the automotive industry, pre-applied coatings are preferred.
One prior method involved the use of a nylon plastic "patch," such as those described by Villo (U.S. Pat. No. 3,093,177). Such patches were applied to a metal member by a process in which a nylon pellet was mechanically applied through the application of heat (as for example, 450.degree. F.) and pressure (as for example, 100 PSI), and thereby fused to the metal surface. As will be perceived, this method required high temperatures and pressure, and thus was not suitable for many applications. Several later alternatives to the use of a nylon pellet have been developed, such as the creation of the patch by spraying powdered nylon and a primer epoxy resin (pre-applied or mixed as a powder with the nylon powder) onto the fastener preheated to a temperature sufficient to melt the powder (e.g. U.S. Pat. Nos. Re 28,812 and 3,787,222).
An alternative adhesive system was developed by Wallace (U.S. Pat. No. 4,285,378). The Wallace method employed a resin powder (preferably nylon and/or teflon) and an activator capable of reacting to polymerize the resin into an essentially solid, non-tacky resilient deposit. The Wallace method had the advantage that the material could be applied to the metal surface cold and, thus, that it was not necessary to use temperatures approaching the melting or fusing temperature of nylon. Nevertheless, the physical properties of the epoxy-nylon mixture were sufficiently close to those of aforesaid nylon patch methods so that the friction locking effect was substantially identical to that of a solid nylon patch.
Further alternatives to the nylon patch technology generally fall into three distinct categories: systems using microencapsulated components, systems using non-integral films, and systems using integral films. Adhesive systems which use microencapsulated components may employ either integral or non-integral films. Typically, the improved adhesive systems have employed an epoxy resin and a polymerizing (or "hardening") agent.
Such methods most preferably may be adapted to permit the continuous manufacture of self-locking articles. Rodden et al. (U.S. Pat. No. 4,366,190), for example, describes an apparatus which provides a feeder means to supply threaded articles in substantially continuous succession and a support for conveying such articles along the path for heating the articles and then for applying a heat fusible resin to the articles.
A. Adhesive Systems Which Employ Microencapsulated Components PA0 B. Adhesive Systems Which Employ Non-Integral Films PA0 C. Adhesive Systems Which Employ Integral Films
Adhesive systems have been described which employ microencapsulated components (such as a resin and its curing agent). In such formulations, the encapsulated resin and curing agent do not react until the capsules are broken and the resin and curing agent are able to contact one another. Microencapsulated systems may, depending upon formulation, be advantageous in extending shelf- or pot-life, and in having more desirable break away torques, consistency and reproducibility.
In adhesive systems which employ microcapsules, the resin or hardener is typically mixed with a polymerizing agent, and applied to the metal substrate as a slurry, etc. Methods for microencapsulation are described in U.S. Pat. No. 3,746,068.
Further methods of encapsulation are described by Gorman in U.S. Pat. No. 3,704,264. This patent describes the encapsulation of a homopolymeric composition comprising a core of a liquid monomeric, polymerizable, acrylate ester. The patent teaches that dimethacrylates are suitable for use as the monomeric acrylate esters of the invention. Encapsulation products are prepared by introducing discrete portions of the monomeric compositions into a fluid and then contacting the portions with a polymerization catalyst capable of promoting homopolymerization of the monomeric composition. The portions are removed from the fluid after an encapsulating shell of homopolymer has been formed. The film is formed in situ by encapsulating the monomeric compositions in a shell of the homopolymer. Thus, the Gorman et al. method creates an integral film (i.e. a film whose composition is substantially identical to the composition of the resin or the hardener composition which it covers).
One disadvantage of the Gorman et al. method is that control of particle size and wall thickness (particularly of small microcapsules) is difficult. A second disadvantage of the method is the use of water as a solvent which must be removed (by drying) after formation of the microcapsules. The removal of the aqueous solvent is time consuming and energy inefficient.
A second integral film microencapsulation method is disclosed by Ozono (U.S. Pat. No. 4,588,639). The patent describes microcapsules which contain a hydrophobic acrylate or methacrylate monomer or oligomer capable of polymerization upon exposure to ultra-violet light, a photosensitizer, and a UV screening agent. The microcapsules are dispersed in water to form a colloidal dispersion and exposed to UV light with a fluence sufficient to cure only the surface of the microcapsule. The resulting microcapsules have a core of the microcapsule. acrylate or methacrylate monomer or oligomer encapsulated within a shell of the cured acrylate or methacrylate. Thus, use of the method results in the formation of an integral film. The patent discloses the use of 1,6-hexanediol diacrylate and dimethacrylate as suitable monomers. In order to control the wall thickness, the method requires the use of an ultraviolet screening agent in the compositions.
In contrast, Austin et al. (U.S. Pat. No. 4,228,216) disclose a microcapsule having a hydrophobic, radiation curable, liquid core encased in a non-integral film (i.e. a film whose composition differs from that of the material which it covers). The microcapsules are produced by incorporating a "wall forming" component into the hydrophobic liquid, and forming droplets of this liquid in a hydrophilic emulsion which contains a second "wall forming" component. Reaction between these two "wall forming" components results in the formation of a non-integral skin. The microcapsules can then be cured using radiation, to produce the desired coating.
Hart (U.S. Pat. No. 4,536,524) describes a micro-encapsulated epoxy adhesive system employing a coacervate emulsion containing a hydrophobic curing agent and a microencapsulated epoxy resin. The disclosed microcapsules have a non-integral skin composed of an agent such as a polyvinyl alcohol.
Deckert et al. (U.S. Pat. Nos. 3,642,937 and 3,746,068) disclose a stable, pressure-activatable adhesive system which employs a microencapsulated resin (preferably an epoxy and a non-volatile curative therefore). The resin is encapsulated in a shell of a urea-formaldehyde resin. Thus, the patent discloses the formation of a capsule having a non-integral film. The microcapsules are mixed with a binder matrix which contains a curing agent for the encapsulated resin. This composition may be applied to a surface (such as a bolt, etc.), or may be used as a sheet or on a washer. Upon application of a shearing force to the surface, the capsules are ruptured and the resin thereby comes in contact with the curing agent. The composition additionally contains a binder resin added to provide a formulation which will dry to form a solid, substantially tack-free state.
In systems employing a non-integral film, a thin film is formed on the surface of a pre-deposited epoxy resin or hardening agent by the application of a film forming agent to the surface of the composition containing the resin or the hardening agent. This system thus requires a first coating containing the resin or polymerizing agent, followed by a second coating which contains the film-forming agent. Such a system produces a non-integral film.
Davis et al. (U.S. Pat. No. 4,091,122), for example, describe a process for producing a film over a liquid material using a radiation-curable coating. Although the patent is directed to the use of such coatings to produce "carbonless" paper, it provides a detailed discussion of the use of radiation-curable coatings. Such coatings may be used to form non-integral films over epoxy resins or polymerizing agents. The use of 1,6 hexanediol diacrylate as a radiation curable substance is disclosed.
Lu (U.S. Pat. No. 4,070,398) describes laminates which are produced by coating a metal foil with a radiation-curable composition, in order to form an outer membrane layer.
Yamamoto et al. (U.S. Pat. No. 4,484,204) describes a heat sensitive record material comprising a base sheet and a heat-sensitive record layer formed over the base sheet. A resin layer, cured with an electron beam, is formed over the record layer. A large number of unsaturated polyesters, polyester acrylates or polyester methacrylates, urethane acrylates or urethane methacrylates, epoxy acrylates or epoxy methacrylates, silicone acrylates or silicone methacrylates, polybutadiene acrylates or polybutadiene methacrylates, polyether acrylates or polyether methacrylates, or melamine acrylates or melamine methacrylates may be employed. The patent, in particular, discloses the use of 1,6 hexanediol diacrylate as a useful acrylate monomer in forming the resin layer.
A significant improvement in this art was described by R. B. Wallace in U.S. Pat. No. 4,325,985. This improvement relates primarily to a substantial elimination of the drying time that had been previously required to protect fluid deposits on a thread area of a threaded fastening device. In a preferred embodiment of the invention, adjacent fluid deposits of a two-part adhesive, such as an uncured epoxy resin and a polymerizing agent therefore were permanently protected by a thin, dry, solid, non-tacky, non-integral cover film which was applied immediately after the still-fluid deposit of the resin and polymerizing agent.
The cover film is formed by irradiating a UV-curable film forming material with ultra-violet light. The improved method permitted the use of much lower temperatures than had been possible with earlier methods.
Further improvements in non-integral film adhesive systems were disclosed by R. B. Wallace in U.S. Pat. Nos. 4,686,272 and 4,764,579. The Wallace U.S. Pat. No. 4,764,579 patent describes a method for producing a fluid, self-curing or setable adhesive for general application. The adhesive system comprises a mixture of a multiplicity of small, discrete, contiguous deposits of a first fluid containing an uncured but curable fluid resin, and a second fluid comprising a fluid of curing agent for the particular resin. The contiguous deposits were separated by a thin, flexible, and rupturable protective film barrier formed in situ by reaction of the fluid resin and the fluid curing agent. Since the film barrier differs in composition from either the fluid resin, or the curing agent, the method exemplifies a non-integral film adhesive system.
In order to effect adhesion, the adhesive system described in the Wallace U.S. Pat. No. 4,764,579 patent must be kneaded or mixed under force sufficient to rupture the barrier film. A divisional of the U.S. Pat. No. 4,764,579 patent (Wallace, U.S. Pat. No. 4,686,272) is directed to the fluid adhesive mixture, per se.
Significantly, the Wallace U.S. Pat. No. 4,764,579 method permitted one to limit the thickness of the barrier film that was formed by the reaction between the resin and the activator or curing agent. The method permitted one to form very thin barrier membranes.
The Wallace U.S. Pat. No. 4,764,579 patent discloses the use of the compositions in enclosures such as the recess in a wire nut (Stockwell, U.S. Pat. No. 2,825,750).
The formulations of the present invention may be used in the conventional wire nut of Stockwell, or in another, alternative wire nut design: i.e. a "butt connector" capable of joining two wires, end-to-end. Typically, such a "butt-connector" will comprise an inner crimpable metal tube covered by a semi-rigid vinyl sleeve. The wires which are to be joined are typically inserted into each end, and the tube is crimped closed through the flexible sleeve with, for example, a crimping tool or pliers, thus locking the wires in place. Examples of "butt-connectors" are disclosed by Wetmore (U.S. Pat. No. 3,243,211), Reeder (U.S. Pat. No. 3,944,721), Fava (U.S. Pat. No. 3,852,517), Holt (U.S. Pat. No. 4,553,809), and, in particular, Fitch et al. (U.S. Pat. No. 4,778,984), Clabburn (U.S. Pat. No. 3,721,749), Hess (U.S. Pat. No. 3,360,631), Siden et al. (U.S. Pat. No. 3,945,114), and Dewdney (U.S. Pat. No. 3,930,606).
Use of the present invention provides a means for protecting both the conventional Stockwell wirenut, and for a novel "butt-connector" described below from corrosive elements. In the novel "butt-connector" of the present invention, the vinyl sleeve is eliminated, and the wires are crimped in the bare metal tube. Around the crimped metal tube is placed a coffin-like case (preferably nylon), having a cover hinged to a receptacle for the metal tube, and possessing a suitable hole at each axial end for the wires extending from the crimped tube. Most preferably, the case would lock on closing, through the presence and action of a barbed ridge at the closing edges of the receptacle and the cover. The center area of the case is enlarged, and contains the photo-skinned resin and hardener compositions of the present invention. Desirably, the skins of the compositions would immediately rupture and be extruded axially as the hinged cover is closed onto the receptacle. Preferably, the case would then be rotated along the axis of the metal tube/wires, in order to further mix the compositions, and to enhance their distribution around the exposed areas at the ends of the metal tube.
Although the above-described non-integral film adhesive systems have a number of advantages over liquid products in ease and speed of assembly, they have a number of shortcomings: the binder used is frequently not an integral part of the final polymerized film and the resulting strength is therefore not as great as that of a film from the monomer alone, such as is obtained from a polymerizable liquid product. Non-integral films cause the friction of assembly to be increased, thus adversely affecting the torques/tension relationship so that the tension achievable in a fastener for a given torque is less than that achievable for an uncoated fastener. Stripping of the film can occur, particularly on some surfaces with ill fitting or burred nuts with consequent failure of the locking system. The coating is either deposited from organic solvent which is expensive and wasteful in operation and is normally a health and safety hazard, or is deposited from aqueous emulsion, but in this event ovens for drying are necessary which are expensive in capital requirements and in energy of operation.
In systems which employ integral films, the film is an integral part of the composition, and is in intimate association with the epoxy resin or hardening agent of the adhesive (or lock-forming material). The material is treated to form a thin film on the surface of the epoxy or polymerizing agent deposit. Typically, in such systems, an opacifier agent is added to the compositions in order to control film thickness.
Thompson (U.S. Pat. No. 4,632,944), for example, describes a polymerizable fluid for sealing and locking engineering parts. Sealing is mediated after a coating of the fluid is applied to an engineering part. Sealing is achieved by free-radical initiated polymerization of the same monomer that ultimately comprises the final cured film, and results in the formation of an integral film. This first film forming step (free radical initiated polymerization) is initiated by radiation (such as by UV light). An opacifier (such as a powder dispersed in the fluid) must be added to the polymerizing composition to limit the depth of polymerization to the formation of a film only. The polymerization reaction creates a dry, tack-free skin, but due to the presence of the opacifier, radiation is obstructed from passing beyond the surface layer. Thus, fluid below the surface layer is unaffected by the radiation.
A second curing of the remaining liquid monomer below the skin is accomplished through the use of a free radical induced addition polymerization. Polymerization is initiated when two engineering parts are assembled together.
The adhesive system disclosed by Thompson contains five essential elements. The polymerizable monomer is an acrylic or methacrylic ester. The use of acrylate or methacrylate esters of a monohydric, dihydric, trihydric or polyhydric alcohol, such as n-hexanol, ethoxylated bisphenol A, trimethylol propane, or pentaerythritol, is explicitly taught. The second component of the system is a photoinitiator which is a free radical polymerization catalyst such as a benzoyl peroxide. The third element of the system is an activator which is a tertiary amine such as a substituted aniline or a heavy metal such as copper, lead etc. The fourth component of the system is a photoinitiator which absorbs energy at a certain wave length and leads to the cross-linking of the polymerizable monomer. The use of benzoin ethers, benzil, and similar agents are disclosed. The fifth element of the composition is the opacifier which is a finely divided powder opaque to incident radiation. The use of a pigment or extender or a metal powder is explicitly taught.
A further improvement in adhesive systems was developed by R. B. Wallace and is disclosed in U.S. Pat. No. 4,847,113. Whereas, as described above, prior methods had employed a subsequent UV curable coating material to encase the resin and its curing agent on a substrate, the method of the Wallace U.S. Pat. No. 4,847,113 patent provided a means for mixing the resin or curing agent with a UV curable material and then accomplishing the application of the material to the substrate in a single, rather than double application. In one embodiment, two fluid applicators apply two different liquids, each to different locations on the fastener. Each has in it a UV curable material. One has a curable resin in it, while the other has a hardener for the resin. The curable resin is not polymerizable by UV light; only the UV curable material is. In a typical apparatus, the fastener now having the two separated liquid patches on it, is moved to a second station where the deposited material is subjected to irradiation with ultra-violet light. This ultra-violet irradiation cures the UV curable material resulting in the formation of a flexible, dry, non-tacky and continuous, integral film or skin over the two deposits of curable resin and hardener, respectively. No opacifier is necessary in such a system since the depth of UV cure is adequately controlled by adjustment of the parameters of operation. Microencapsulation of the hardener within the liquid resin is also taught, such that only one patch need be applied, if desired. In either instance, fastening the fastener (nut to bolt) breaks the skin and mixes the hardener with the curable resin, thus effecting its cure.
The Wallace U.S. Pat. No. 4,847,113 patent discloses that a variety of UV curable monomers may be employed, but that a particularly good monomer for the purposes of that invention was trimethylopropane triacrylate (TMPTA). Any of a variety of photoinitiators (including ketones, benzophenones, aromatic ketones, and the like) may be employed. The curable, non-UV sensitive resin is preferably a commercially available epoxy (such as a bisphenol A epichlorohydrin resin). The Wallace U.S. Pat. No. 4,847,113 patent discloses the use of tertiary amines as effective curing agents for the epoxy resin. It has been found, however, that while an excellent product is formed using TMPTA, the shelf life of the applied hardener patch was somewhat limited, in that after a certain period (approximately six weeks) the hardener patch would become waxy and dry, even though the separate epoxy patch beneath the surface of the skin remained liquid. In an attempt to lengthen the shelf life, numerous hardeners were attempted, as listed below, but to no avail:
__________________________________________________________________________ PRODUCT NAME CHEMICAL SUPPLIER __________________________________________________________________________ NC-540 CARDOLITE CO. NC-541 CARDOLITE CO. CAPCURE 40 HENKEL PROCESS CHEM. CO. ACTIRON NX-3 SYNTHRON INC. HARDENER XU-HY-195 CIBA GEIGY BORON TRIFLUORIDE DIHYDRATE CIBA GEIGY PRIMER HP12 HERON MFG INC. NADIC BUFFALO COLOR CORP. CAPCURE 40 HENKEL CAPCURE 1.5 HV HENKEL HARDENER HY9225 CIBA GEIGY NC 513 CARDOLITE CO. ACRYLIC STRUCTURAL ADHESIVE VERSICOK ANCAMINE K-54 PACIFIC ANCHOR CHEM. CORP. NC 514 CARDOLITE CO. EPON CURING AGENT H-1 SHELL CHEN. CORP. HARDENER HT 939 CIBA GEIGY ANCAMINE K-618 EPOXY HARD. PACIFIC ANCHOR CHEM. CORP. ACTIRON NX-3 POWDER SYNTHRON INC. ACCELERATOR DY 064 CIBA GEIGY ACCELERATOR 225-B LORD CORP. FURSOR EPOXY ADHESIVE CURING AGENT 322 LORD CORP. VERSALOC 2258 LORD CORP. AZAMINE 1229 SHEREX POLYMERS ANCHOR K-54 PACIFIC ANCHOR HARDENER HY850 CIBA GEIGY NC-1307 CARDOLITE HARDENER NY 837 CIBA GEIGY HARDENER XU-HY-350 CIBA GEIGY N-(ISOBUTOXYMETHYL) ACRYLAMIDE AMERICAN CYANAMID CO. ANCHOR 1173 PACIFIC ANCHOR EPON CURING AGENT V-15 SHELL CHEM. CO. HARDENER HT 939 CIBA GEIGY EPON CURING AGENT U SHELL CHEM. CO. ANCHOR 1170 PACIFIC ANCHOR ACTIRON NXJ-60 SYNTHRON INCORP. ANCHOR 2044 PACIFIC ANCHOR ANCAMINE XT PACIFIC ANCHOR ANCAMINE AD PACIFIC ANCHOR VERSAMIDE 280875 HENKEL ANCAMINE 1769 PACIFIC ANCHOR ANCAMINE 1110 PACIFIC ANCHOR 1,3-DI-4-PYRIDYLPROPANE NA 2 ETHYL-4-METHYLIMIDAZOLE NA 4-METHYLIMIDAZOLE NA 1,2-DIMETHYLIMIDAZOLE NA 1 METHYLIMIDAZOLE NA 1,6-HEXANDIAMINE NA DIETHYLAMINE NA 4,4 TRIMETHYLENEDIPIPERIDINE NA MALEIC ANHYDRIDE NA N-METHYLDIETHANOLAMINE NA 4-METHOXYPHENOL NA TRIBUTYLAMINE NA DIETHANOLAMINE NA IMIDAZOLE NA __________________________________________________________________________
Ideally, a fastener-locking system should be capable of easy manufacture or assemblage by the user. It should be tack-free and sufficiently secure against inadvertent mixing of the resin and curing agent so that many fasteners can be shipped and stored in barrels or other containers without adhering to each other or becoming tacky to the touch. The adhesive system should be deposited on the fastener as a dry-to-touch coating in which polymerizable fluids are incorporated and so that the action of assembly causes the components to mix with one another thereby causing polymerization of the fluids and locking and sealing of the assembly. The adhesive applied to the fastener should have long term stability after application and film formation (i.e. a long "shelf-life") so that the coated fastener may be handled and stored in accordance with conventional procedures without degrading the adhesive until used. In use, the fastening device should be capable of being readily applied without undue increase in the amount of work or input torque necessary to install the fastener. The adhesive should cure rapidly so that the fastener may be used after only a short cure period and provide a bond, such that substantially increased work or back off torque is required to remove the fastener. Desirably, also such a system should, in certain instances, be capable of reuse after removal of the fastener and the adhesive should provide some curing which would enable a fastener which has slightly loosened due to vibration or other stresses, to become refastened rather than dropping out of place.
Many of the above attributes are realized by the previously described invention of Wallace U.S. Pat. No. 4,847,113. The present invention, however, further expands upon the significant improvement of the Wallace U.S. Pat. No. 4,847,113 patent by providing formulations capable of providing even greater "shelf-life" and flexibility of use than those disclosed in the aforementioned patent. In addition, the compositions of the present invention exhibit a greater speed of cure, and have the advantage that they are stable to high heat. The significance of these advantages is discussed below.
It is thus an object of the present invention to provide an integral skin adhesive system, having enhanced shelf life, and being useful to seal and/or lock two substrates to one another.